Epeak estimator for gamma-ray bursts observed by the swift burst alert telescope

T. Sakamoto*, G. Sato, L. Barbier, S. D. Barthelmy, J. R. Cummings, E. E. Fenimore, N. Gehrels, D. Hullinger, H. A. Krimm, D. Q. Lamb, C. B. Markwardt, D. M. Palmer, A. M. Parsons, M. Stamatikos, J. Tueller, T. N. Ukwatta

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

68 Citations (Scopus)


We report a correlation based on a spectral simulation study of the prompt emission spectra of gamma-ray bursts (GRBs) detected by the Swift Burst Alert Telescope (BAT). The correlation is between the Epeak energy, which is the peak energy in the νFν spectrum, and the photon index (Γ) derived from a simple power-law (PL) model. The Epeak- Γ relation, assuming the typical smoothly broken PL spectrum of GRBs, is log Epeak = 3.258-0.829 Γ (1.3 ≤ Γ ≤ 2.3). We take into account not only a range of Epeak energies and fluences, but also distributions for both the low-energy photon index and the high-energy photon index in the smoothly broken PL model. The distribution of burst durations in the BAT GRB sample is also included in the simulation. Our correlation is consistent with the index observed by BAT and Epeak measured by the BAT, and by other GRB instruments. Since about 85% of GRBs observed by the BAT are acceptably fit with the simple PL model because of the relatively narrow energy range of the BAT, this relationship can be used to estimate Epeak when it is located within the BAT energy range.

Original languageEnglish
Pages (from-to)922-935
Number of pages14
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2009 Mar 1


  • gamma rays: bursts

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics


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